Abstract

Dental enamel manifests high transparency in the near-IR. Previous work demonstrated that near-IR light at 1310-nm is ideally suited for the transillumination of interproximal dental caries (dental decay in between teeth) [1]. However, most new dental decay occurs in the pits and fissures of the occlusal (biting) surfaces of posterior teeth. These caries lesions cannot be detected by x-rays during the early stages of decay due to the overlapping topography of the crown of the tooth. In this study, a near-IR imaging system operating at 1310-nm was used to acquire occlusal images by launching the near-IR light into the buccal surface of the tooth just above the gingival margin (gum-line). The near-IR light diffuses through the highly scattering dentin providing uniform back illumination of the enamel of the crowns allowing imaging of the occlusal surfaces. The near-IR images show high contrast between sound and demineralized areas. Demineralization (decay) can be easily differentiated from stains, pigmentation, and hypomineralization (fluorosis). Moreover, the high transparency of the enamel enables imaging at greater depth for the detection of subsurface decay hidden under the enamel. These early images suggest that the near-IR offers significant advantages over conventional visual, tactile and radiographic caries detection methods.

Occlual image contrast model, areas of occlusal decay appear darker as diffuse light from within the tooth is attenuated by occlusal caries. (A) shallow caries in fissures, (B) caries that penetrate deep and spread in the underlying dentin may create a larger opacity on the FPA.

(A) Reflected light image (visible) of molar with extensive flourosis and a large lesion (yellow circle) in the central pit, (B) Radiograph (D-speed film), (C) NIR image of tooth, the lesion is the large opacity in the yellow circle.

Premolar with a hidden subsurface lesion, the reflected light image (A) contains a deep, pigmented fissure, but it is not clear whether there is decay. (B) Radiograph (D-speed film) shows no decay. The NIR image (C) contains a large opacity in the yellow square. The tooth was cut in half along the dotted line in (C), and the tooth hemi-section (D) shows the lesion at the base of the pit (red circle). Note that there is no decay along the walls of the fissure. The decay does not show up very well in the PS-OCT parallel axis scan (E) taken transverse to the fissure while the PS-OCT perpendicular axis scan (F) clearly shows the decay at the base of the pit. Areas of high reflectivity are in red, moderate reflectivity in white, and low reflectivity in blue in the PS-OCT scans.

Molar with an extensive network of fissures (A) the reflected light image shows dark areas that may be either stains or demineralization (B) NIR image shows that some fissures have demineralization and others are sound or normal.